The invention relates to a navigation device with a housing, an antenna, forming a part of the device, for position signals, an internal conversion unit for evaluating and converting the received position signals into digital position information, a central processing unit with a navigation interface for receiving and for processing the digital position information and with a data input via which an external receiving antenna with an external conversion unit can be connected for generating digital position information.
Such navigation devices are known. Due to their internal antenna for the position signals, particularly satellite position signals (in the GPS or GLONASS systems current at the present time or in future systems such as, for example, the intended GALILEO system, the navigation devices can be operated autonomously. Accordingly, the use of such navigation devices is also possible in motor vehicles which are not equipped with a corresponding satellite antenna, or outside a motor vehicle such as, for example, when riding bicycles, hiking, etc. The problem with autonomously using the navigation device in a motor vehicle is, however, that due to the shielding effect of the metallic motor vehicle chassis, the internal antenna, that is to say the device itself, must be arranged at a position which, on the one hand, provides for adequate reception of the high-frequency satellite position signals and, on the other hand, for good legibility of indications on a display normally present. The possible compromises existing for this purpose normally do not allow optimum reception so that, particularly in difficult reception situations due to shading, etc., the required updating of the current position sometimes does not take place.
It is known, therefore, to use an external satellite antenna which is combined with a conversion unit, which is also external, in order to evaluate the high-frequency satellite position signals and to convert them into digital position information. This position information can be transferred without interference to the navigation device when the navigation device is equipped with a corresponding data input, preferably in the form of a USB input, in order to receive the digital position information via this data input.
Such a satellite antenna with its own conversion unit (for the GPS system) is also called GPS mouse.
In the known navigation device of the type initially mentioned, the digital position information formed by evaluation and conversion can thus be present which has been received by the internal satellite antenna or by the external satellite antenna. It is known to conduct the digital position information formed to two interfaces of the central processing unit, wherein the central processing unit preferably processes the input signal at the interface allocated to the external satellite antenna. Since two interfaces of the central processing unit must be reserved for the digital position information, a standard use of this central processing unit provided for the reception of digital position information at only one interface is not possible.
As an alternative, it is known, in principle, to provide high-frequency antenna signals, for example broadcast signals, with an antenna belonging to the device and an external antenna connected to an antenna input. In this arrangement, the switch-over is performed in such a manner that the high-frequency signal of the external antenna is converted and processed when a connection has been made to the antenna input. The problem in this arrangement is the required careful conduction of high-frequency signals to the antenna input when the external antenna is arranged at some distance to the device itself, as is frequently appropriate.